In The Promise of Near Real-Time Application Simulation in the Cloud I described how Simz can create something out of nothing when no process exists for an application that is dynamically managed in the cloud. The same article also showed how Simz can make multiple application runtimes look like a single one. But in the early inception of Simz we had another equally powerful use case in mind and that was to have a runtime simulation for every actual application runtime.

Simz in this context resembles a (black box) flight recorder, but instead of storing sampled sensor data it replays in unison the metered execution behavior, recorded and transmitted from the real runtime via a live metering feed. If the application runtime suddenly terminates, and closes the connection feed, we can still acquire runtime diagnostics from the simulation. More importantly the stack of each simulated thread will reflect what was in the process of being executed, but not completed, before an abrupt termination. This also addresses the issue where diagnostic routines built into the runtime, called via shutdown hooks, are not able to execute in time before the process is completely ended.

We can take this further by incorporating elements of behavioral supervision and behavioral memorization. Process level supervision is a familiar concept for those working with actor based languages and runtimes such as Erlang/OTP....

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